The present invention relates generally to laser beam projectors and telescopes, and more specifically to a gimbaled phased array projector/telescope.
A synthetic aperture is formed when separate optical systems are combined to function as a single larger aperture. When a telescope aperture is synthesized, independent optical systems are phased or adjusted to provide a common optical path length from the object to the focal plane. This results in a system in which all the independent optical elements form a common image field with resolution determined by the maximum dimension of the array and therefore exceeding that produced by any single element. Likewise, by optically phasing an array of multiple laser beam projectors, a synthetic aperture is formed which can achieve the performance of an equivalent sized, single laser transmitter.
While the use of multiple laser projectors in a synthetic array has a number of advantages, this use also poses a problem in that the multiple laser projectors (each being an element in the array) must be brought into phase with each other. This task becomes complicated when the array is in the process of tracking one or more moving targets.
The term "Self Compensating Phase Control" is a name for the approach to use the rotation of each array element (e.g., projectors or telescopes) in the phased array to provide most of the large optical path length shift required for phasing during a phased array look angle shift by individual telescope slew (i.e. venetian blind steering). The optical train configurations of conventional systems requires a relatively large amplitude of adjustment in the piston control mirror if an equal optical path length is to be maintained from object to sensor for a telescope or laser to target for a laser projector across all of the elements in the array.
The task of adjusting the phase and optical path lengths of multiple laser projectors which form an array which tracks moving targets is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are specifically incorporated by reference.
______________________________________ U.S. Pat. No. 4,639,586 issued to J. Fender et al; U.S. Pat. No. 3,898,639 issued to H. Nuncheryan; U.S. Pat. No. 3,359,581 issued to L. Lipschutz et al.; U.S. Pat. No. 4,417,253 issued to H. Jacky; U.S. Pat. No. 3,961,334 issued to C. Whitby et al; U.S. Pat. No. 4,087,162 issued to F. Kuffer; U.S. Pat. No. 3,419,898 Baldwin et al.; and U.S. Pat. No. 4,165,936 Eisenring et al. ______________________________________
The subject matter of this application is related to the subject matter contained in the U.S. Pat. No. 4,639,586 issued Jan. 27, 1987, entitled "Optically Phased Laser Transmitter" by Janet Fender et al.
U.S. Pat. No. 3,898,639 discloses a security surveillance laser system having a plurality of laser beams steered by mirrors in parallel paths. U.S. Pat. No. 3,359,851 discloses a multiple beam interferometer which includes a plurality of filters and mirrors for directing a particular component of a reflected light beam to an associated camera. U.S. Pat. Nos. 4,417,253; 3,961,334; 4,087,162; 3,419,898 and 4,165,936 each discloses beams of light being steered by a plurality of mirrors.
The present application hereby incorporates by the patent of Janet S. Fender et al., entitled "Optically Phased Laser Transmitter", U.S. Pat. No. 4,639,586. The apparatus of the Fender et al. patent is a laser transmitter which optically phases the output of an array of multiple optical laser telescopes to achieve the performance of a single laser transmitter of equivalent size.
The Fender et al. apparatus performs wavefront phase matching between pairs of laser beams using an array containing at least two optical telescopes which become useable as a laser beam transmitter when combined with an optical wavefront phase matching system consisting of a collecting telescope, a detector array, two fold mirrors, analog-to digital converter, microprocessor, and two sets of correcting mirrors.
The two optical telescopes are adjacent to each other, and transmit two separate outgoing laser beams which require phase matching. The original source of the two outgoing beams may be either: a single laser beam, which has been divided (monochromatic); or two separately generated but coherent laser beams.
The collecting telescope sits in front of the two optic telescopes and bridges the gap between them. In this way, the collecting telescope is able to intercept samples of outgoing laser beams from the edges of both telescopes and focus them through the two fold mirrors to the detector array.
The detector array may be either a line scan or an area charge coupled device (CCD), which reads out the fringe pattern by generating an interference pattern. The microcomputer controlled image processor receives the interference pattern between samples of pairs of transmitted laser beams from the CCD camera, then performs a calculation of the difference in phase of the wavefronts between the two teams. This allows the laser transmitter to match the phase of the outgoing beams by adjusting the optical path lengths using the correcting mirrors which trombone to increase or decrease the optical path length as required.
While the system disclosed in the above-cited references are instructive, a need remains to provide a mirror configuration for self-compensation of a laser beam phase mismatch in an array which occurs while retargeting the beam. The present invention is intended to satisfy that need. The present invention also provides a system which greatly reduces the amplitude of adjustment required in the piston control mirror while maintaining an equal optical path length from the object to the sensor for a uniform laser beam phase across all of the elements in the array.